Study on ZnO-based gas sensor for detection of acetylene dissolved in transformer oil

Abstract

Acetylene (C 2 H 2 ) is one of the most important and typical characteristic fault gas dissolved in power transformer oil, and on-line monitoring its concentration could reflect the operational state of transformer timely, which could prevent safety issues of power grid effectively. Considering the traditional zinc oxide (ZnO) gas sensor exhibiting some shortcomings, such as higher operating temperature, lower response, poor selectivity, and so on. The paper proposes the ZnO-based (pure ZnO, cobalt-doped ZnO) gas sensors to contrastively study. The characterization results of nanomaterials (XRD, FESEM, HRTEM) show that the as-grown products possess the good crystal structure and high purity. The gas-sensing experiment results on optimum working temperature (Co-ZnO: 160 °C, pure ZnO: 180 °C), response-recovery time (Co-ZnO: 30–33 s, pure ZnO: 35–51 s), sensitivity (Co-ZnO: 9.886, pure ZnO: 1.971; 200 ppm C 2 H 2 ), the limit of detection (3 ppm, Co-ZnO), stability (20, 50, 100, 200, 400 ppm C 2 H 2 ), and selectivity (H 2 , CH 4 , C 2 H 2 , C 2 H 4 ; 50, 100, 200 ppm) are obtained. They correspond to the theoretically analysis which based on the DFT-D calculations. The result of gas-sensing properties indicates that the dopant of Co is beneficial to reduce the optimum working temperature and response-recovery time significantly. In addition, it enhances the sensitivity of gas sensor evidently and process a good stability as well as selectivity. The orbital hybridization occurred during C 2 H 2 adsorption, which promotes the electron transfer and conductivity changes. The results lay a solid foundation for the preparation of new ZnO-based gas sensor that serve for the transformer condition monitoring and fault diagnosis.